1. Field of the Invention
The present invention relates to a display device and a touch sensing method thereof, and more particularly, to a display device with a built-in touch sensor and a touch sensing method thereof.
2. Discussion of the Related Art
With the advancement of various portable electronic devices such as mobile terminals and notebook computers, the demand for flat panel display devices applied to the portable electronic devices is increasing.
Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, light emitting diode (LED) display devices, and organic light emitting diode (OLED) display devices have been developed as flat panel display devices.
In such flat panel display devices, LCD devices are easily manufactured by advanced manufacturing technology and have drivability of drivers, low power consumption, high image quality, and a large screen, and thus, the application fields of the LCD devices are being expanded. LCD devices, including a built-in touch screen that enables a user to directly input information to a screen with a finger or a pen, are attracting much attention.
In applying a touch screen to LCD devices, a separately prepared touch panel is conventionally disposed on a liquid crystal panel, but, the LCD devices are recently developed in a type where the touch screen is built in a liquid crystal panel for slimming.
Especially, LCD devices using the existing elements, such as common electrodes formed in a lower substrate, as touch sensing electrodes are called in-cell touch type LCD devices.
In the in-cell touch type LCD devices, a plurality of common electrodes formed in a lower substrate (TFT array substrate) are used for display, and moreover used as touch electrodes. In this case, the common electrodes are divided in units of pixels to configure a plurality of touch sensing blocks.
Specifically, among a plurality of pixels provided in the LCD device, a certain number of pixels (for example, 64×64 pixels) configures one touch sensing block. A plurality of touch sensing blocks are connected to each other in an X-axis direction to configure a plurality of touch driving electrodes, and a plurality of touch sensing electrodes are arranged in a stripe type in a Y-axis direction. The touch driving electrodes may be arranged in the X-axis direction identically to a direction of a gate line, and the touch sensing electrodes may be arranged in the Y-axis direction identically to a direction of a data line.
In this case, a touch driving signal is applied to the touch driving electrodes, and the touch sensing electrodes sense a capacitance change.
In the in-cell type touch LCD devices, display and touch sensing are temporally divided and driven due to a structural characteristic in which a plurality of pixels for display and a touch screen for touch detection are provided together.
During a touch sensing period (non-display period), when a capacitance is changed in a touch sensing block touched by a user's finger, a touch sensing electrode senses the changed capacitance, thereby determining whether there is the user's touch and a touched position.
In the related art, however, when touch sensors are disposed outside a liquid crystal panel, a display function and a touch sensing function are separately performed, and thus are not affected by each other. On the other hand, when the touch sensors are built in the liquid crystal panel, the display function and the touch sensing function are affected by each other. That is, touch sensing driving can affect display driving, or, the display driving can affect the touch sensing driving. This will now be described in more detail with reference to FIG. 1.
FIG. 1 is a view showing a capacitance change in a pixel displaying black and a capacitance change in a pixel displaying white, in the related art in-cell touch type LCD device.
As seen in FIG. 1, a pixel “Black” displaying black and a pixel “White” displaying white differ in alignment of liquid crystal, and thus, a difference between capacitances of a liquid crystal layer occurs.
The capacitance difference between pixels is maintained in the pixels even after a touch sensing period is started, and affects touch sensitivity. The capacitance difference functioning like offset to act as noise to touch sensing is called display to touch crosstalk (DTX).
FIG. 2 is a diagram showing a touch raw data difference between a touch sensing block displaying black and a touch sensing block displaying white in the related art in-cell touch type LCD device.
As seen in FIG. 2, the touch raw data difference between the touch sensing block displaying black and the touch sensing block displaying white is an average of 150. That is, even when there is no user's touch, a touch raw data difference is caused by a difference of display information displayed by a pixel corresponding to a corresponding touch sensing block.
For this reason, when a touch threshold value for detecting whether there is a user's touch is 100, even though there is no user's actual touch, a touch can be sensed.